What are turns and rounds and how long are they each?
In AD&D a turn was ten 6-second rounds during combat.
So when I read in D&D 5e that the Thief's Sneak Attack ability says "Once per turn you can deal an extra 1d6 damage", is this saying that abilities like this (e.g. Sneak Attack, Colossus Slayer, etc.) can be done every 6 seconds (i.e., once a round) or once a turn, i.e. once a minute?
My current understanding is that these abilities can be done once a minute.
But then the PHB describes a turn as an action of some sort in the round. This is where I get a little confused.
I have had discussion about this with my group of players, and I am using 1 minute turns. Am I wrong?
D&D 5e turns are completely different from AD&D turns, and only share the name. The AD&D meaning of “turn” as being ten rounds* in combat time (or ten minutes in exploration time) last appeared in AD&D 2nd edition, and has been eliminated from editions newer than 1999.
In D&D 5e, a turn has the same meaning as it does in a card game or similar: a PC gets their turn to do something within the round. It is not a measure of time, but of opportunity to take actions.
So a rogue can Sneak Attack once per turn within a round, which usually means once per 6-second round. However, if a once-per-turn ability can be used as a Reaction, that means they may use it on their turn and on every other combatant's turn, making for more than once per round. (This usually means at most twice per round though, since there are limits on the number of actions available to a character on their turn and off their turn.)
* Incidentally, AD&D rounds are 1 minute each, not 6 seconds each, which makes an AD&D combat turn 10 minutes long.
Is an AD&D round roughly equivalent to a 5e round in regards to what can be done in it? If these guys were locked in Melee for ~10 minutes each fight, they were more Heroic than I've given them credit for!
@lithas Rounds are the same in game content (you get one chance to act and maybe move), but with the idea that a single attack roll is the outcome of a whole minute of egaging (circling, multiple parries and attacks, etc.) with your chosen foe. But hp totals are low, so combats rarely last more than a few rounds. Combats exceeding a turn are rare and epic. (This also explains where save-or-die effects came from: they worked fine in AD&D because they weren't any different in scale of effect than normal combat.)
All of the above is accurate. It's also worth noting that AD&D's rounds (1 min) were divided in 10 _segments_ of 6 seconds each, during which PC's would act. All in all, in terms of content, we can roughly compare AD&D's **rounds** to 5e **rounds** and AD&D's **segments** to 5e **turns**. The major difference is the duration in which the action occurs : in AD&D, each PC acted once a minute; in 5e, they act once every 6 second (save for reactions).
@Meta4ic I find segments to me more akin to **initiative count** in later editions than to turns. They're not exactly the same (segments are also a time-tracking device for how long actions take during a round or multiple rounds), but it's closer to 5e initiative count than to a 5e turn.
You are mistaken
A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn.
So, according to the Player's Handbook, a turn is at most about 6 seconds long, because a round is comprised of many turns. Beyond this breakdown, it's dangerous to think too hard about what is happening. Remember that combat in D&D is an abstraction, HP represents more than just physical cuts and scrapes, and the order that actions actually occur in a turn is ambiguous at best. Generally at my tables we've played such that turns happen approximately simultaneously within one round, with initiative being a good abstraction to explain why that orc didn't manage to attack (because he died before he could).
To directly talk about sneak attack, a Thief can Sneak Attack not only on every single one of his turns, but he can also do it on his opponent's turns. This might sound very powerful, but keep in mind that Thieves do not get extra attacks, and because they'll be using Finesse or Light weapons to do their dirty work, their damage dice without Sneak Attack are pitiful. You'll quickly notice that a well-played thief will almost always trigger their Sneak Attack during their turn, and that is ok.
Yes and No.
A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn. (PHB 189)
The only thing wrong with the above answer is their definition of a turn, A turn is literally mere moments when compared to the 6 second time-frame of a round. This is counted as a specific ruling, technically. A round is about 6 seconds, meaning that a give or take of 1 second is allowed. So even though a ROUND is 5-7 seconds long, turns are different. A round is defined as a 5-7 second time-frame in which the full order of initiative is acted out until it resets to the highest initiative. You are right in your statement about the approximate simultaneous actions within a round, with the rolled initiative standing as each character's grasp of the situation and their reflexes at that combat instance.
Though no matter that a Round consists of 5-6 seconds, it can be comprised of thousands of Turns if it needs. Just look at massive scale wars. Basically a turn in this mindset is just the character's moment in that 6 seconds to take their actions.
Now on to the Sneak attack part:
Beginning at 1st level, you know how to strike subtly and exploit a foe’s distraction. Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.
Let's break this down now.
Once per turn,
To be precise, this allows the Rogue in question to use their Sneak Attack feature at any turn, not just their own. Nice
you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.
Now this is where the RAW meat is, lol. The effect activates at ANY time your weapon would deal damage, NOT just when you take the Attack Action (which is usually limited to use on your own turn). Here's an example:
If a feature let's this rogue use an attack as a Bonus Action outside their own turn, and the environment fits with the rest of the Sneak Attack description (have advantage, or not needed when a foe of the target is within 5 feet of the target, isn't incapacitate, and you don't have disadvantage), you get to add your Sneak Attack damage the damage inflicted.
Let's say this rogue and his ranger buddy team up on a single Orc (poor orcs are always abused). The ranger is at one end of the hallway while the rogue sits in an alcove out of site of the target Orc. The rogue is effectively hidden because of full cover, the orc might know there is something there but can not discern the exact location. The rogue then uses Cunning Action to Hide as a Bonus action. The ranger can then fire at the Orc to get it's attention and the Orc charges the ranger. The second the Orc attempts to leave the space right beside the hidden rogue, since almost all rogues will roll a higher Stealth than an Orc's passive perception, they can use their Sneak Attack along side their Reaction to get an Attack of Opportunity on the passing Orc.
There might be more instances of using an attack outside of your own turn, but without a book directly in front of me (only my character sheet), I can not give every example of how a sneak attack can be used.